Various wrapping apparatuses have been commercially available which are capable of wrapping loads such as a stack of corrugated cardboard boxes with a very thin plastic film while stretching the plastic film. A typical example of such an apparatus has a turntable for carrying the load, a supporting post which is spaced apart a predetermined distance from the turntable and carrying a film roll, and primary and secondary rollers which are spaced apart from each other and through which the plastic film unrolled from the film roll is delivered while being preliminarily stretched by these rollers. Namely, the plastic film is stretched between the primary and secondary rollers which rotate at different peripheral speeds and is then wound around the load on the rotating turntable, thereby wrapping the load.
In this known apparatus, if the height of the load on the turntable is greater than the width of the film, it is necessary that the film is frequently moved up and down relative to the load during wrapping so that the film is wound a plurality of times with partial overlaps between adjacent turns. Another problem is that the load such as a stack of goods tend to be collapsed during winding particularly when the load is small in weight and when the width of the film is much smaller than the height of the load. In addition, a considerably large length of the film is consumed because the film has to be wound in a multiplicity of turns.
Under this circumstance, the present inventors have proposed a wrapping method and apparatus in which the plastic film is also stretched laterally to a value which approximate the height of the article as much as possible immediately before the wrapping, thereby overcoming the above-described problems of the prior art.
In this proposed apparatus, a pair of stretching rollers are disposed between the load and the film roll, the stretching rollers having alternating peripheral ridges and peripheral grooves and arranged such that the peripheral ridges and grooves of both rollers mesh with each other. In operation, the plastic film pulled out from the film roll is passed through the nip between the meshing ridges and grooves of both stretching rollers while the stretching rollers are driven at different speeds, whereby the film is stretched both laterally and longitudinally. Then, the stretched film is spread laterally to a greater width and the load is wrapped with this film having an increased width. The lateral spreading of the film is conducted by spreader means capable of gripping both breadthwise ends of the film. The spreader means is so constructed that the angle of divergence of the spreader means is controllable in accordance with the increment of the width attained by the stretching operation.
The amount of stretching is adjustable by varying the distance between both stretching rollers, i.e., the state of meshing between peripheral ridges and peripheral grooves of both rollers. A change in the amount of lateral stretching essentially requires a readjustment of the angle of divergence of the spreder means for the purpose of varying also the degree of spreading. Hitherto, a special device has been required for effecting such an adjustment of the angle of divergence. Furthermore, the known spreader is complicated in construction and is difficult to handle when, for example, setting the film thereon.